Older people with low levels of vitamin B12 in their blood may be more likely to develop problems with their thinking skills and have more brain shrinkage, a new study suggests.

A growing body of research is drawing a link between low B12 and early cognitive decline, a condition that often leads to dementia.

Previous research has found that those people with high levels of vitamin B12 in their blood have lower levels of an amino acid called homocysteine, which some studies have linked to an increased risk of Alzheimer's disease, memory loss, and stroke.

This new study looked at 121 people over the age of 65 in Chicago. Researchers analyzed their blood for levels of vitamin B12 and B12-related metabolites that can indicate a B12 deficiency.

The participants also took tests measuring their memory and other cognitive skills.

After an average of four-and-a-half years, the researchers had the participants do the cognitive tests again. They also took MRI scans of the participants' brains to measure their total brain volume and look for other signs of brain damage.

They found that having high levels of four of five markers for vitamin B12 deficiency was associated with having lower scores on the cognitive tests and smaller total brain volume.

On the cognitive tests, the scores ranged from -2.18 to 1.42, with an average of 0.23. For each increase of one micromole per liter of homocysteine, the cognitive scores decreased by 0.03 points.

The results appear in the journal Neurology.

According to Health Canada, the recommended daily allowance of vitamin B12 for adults is 2.4 micrograms. More information can be found on the Health Canada website.

Interestingly, the concentrations of all vitamin B12–related markers were linked with better cognitive test scores and higher total brain volume -- but not the blood levels of vitamin B12 itself.

Study co-author Dr. Martha Clare Morris, of Rush University Medical Center, said low vitamin B12 can be difficult to detect in older people when looking only at blood levels of the vitamin.

"Looking for vitamin B12 in blood not a good marker," she told CTV News. "We need to have better clinical measures to identify people who have marginal or low vitamin B status."

She said doctors should be testing instead for homocysteine levels. She also said there wasn't enough evidence yet to recommend that all seniors take the vitamin in supplement form.

It's something geriatrician Dr Howard Dombrower -- who works at Markham Stoffville Hospital -- is considering based on the study.

"It's normal for a geriatrician family doctor to prescribe B12 in memory decline if it is low. We might want to consider testing for these other products as well, like homocysteine."

Dr. Howard Dombrower added, "We might be missing a lot of people who do have B12 deficiencies. Even though their serums looks normal their bodies would still be deficient, and we would only know that by measuring these other chemicals."

A Study published last year from the United Kingdom found that giving supplements to older patients with signs of cognitive impairments appeared to slow brain shrinkage, and also appeared to steady cognitive decline. Researchers are hoping to start more testing next year.

But Morris said doctors are not advocating that seniors start taking B vitamins to prevent dementia.

"It's too early to say whether increasing vitamin B12 levels in older people through diet or supplements could prevent these problems, but it is an interesting question to explore," she noted.

Hughene Boggs, on the other hand, swears by her regular B12 injections, prescribed by her doctor four years ago. She is 89 and works full-time running Eden Manor retirement home in Downtown Toronto.

"I can honestly say that I honestly feel sharper than when I was 21 years old," she said.

Boggs has had a B12 injection once a month for the past four years.

"After I have taken my vitamin B12 I definitely feel very much better than I did before in every way, mentally and physically," she said.

Vitamin B12 is found only in animal foods and other foods, such as cereal, that have been fortified with it. It's found in rich supply in organ meats, such as liver, as well as oysters, and found in smaller amounts in meat, poultry, fish, milk products and eggs.

Older people tend to have trouble absorbing the vitamin from food, because of changes to their digestion as they age. Those with celiac disease, Crohn's disease or diabetes also have trouble absorbing it.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip